This invention relates generally to technological advances in the medical field and systems and procedures for prolonging and improving human life. More particularly, this invention relates to a method and system for moving a miniature multi-leaf collimator which remains attached to a linear accelerator or other source of radiation to provide alternative modes of radiation beam shaping. In one mode the beam shaping is determined by the miniature multi-leaf collimator when the collimator is positioned within the beam projection that emanates from the radiation source. In a second mode the beam is defined by another collimator system when the miniature multi-leaf collimator is positioned out of the beam projection. Thus, two alternate fields can be achieved for a fixed patient position and radiation beam position by movement of the miniature multi-leaf collimator without removing the collimator from the radiation device.
Computer-controlled, motorized, mechanical multi-leaf collimators have been applied to produce conformal shaping of radiation beams. By way of example, the multi-leaf collimator for linear accelerators (LINAC""s) are available from Varian, Inc. (Palo Alto, Calif.) and Siemens Oncology Care Systems, Inc. (Concord, Calif.). Such multi-leaf collimators typically have tungsten leaves with widths of approximately one centimeter. The multiple tungsten leaves provide conformal beam shaping of X-ray beams from the LINAC. Conformnal radiation doses can be achieved using multi-leaf collimators to conform more closely to a target volume such as a tumor in the patient""s body.
Miniature multi-leaf collimators (MMLCs) are also used for finer confirmation of radiation beams. By way of example, the miniature multi-leaf collimator from Radionics, Inc. (Burlington, Mass.) and the M3 micro multi-leaf collimator from BrainLAB GmbH (Munich, Germany) provides finer beam confirmation than standard multi-leaf collimators, such as those referenced above from the Varian and Siemens companies. The leaf widths for a miniature multi-leaf collimator are typically thinner than those for a multi-leaf collimator. For example, the MMLC of Radionics, Inc. has tungsten leaves of four millimeter thickness. The miniature multi-leaf collimators are mounted and de-mounted from the linear accelerator during application. When finer confirmation for stereotactic radiosurgery or conformal stereotactic radiotherapy is desired, the miniature multi-leaf collimator can be mounted and secured to the radiation head of a LINAC. When the treatment is completed, the miniature multi-leaf collimator can be removed from the linear accelerator. In some cases, a micro multi-leaf collimator may be permanently mounted in a fixed position on a LINAC. See, for example, the NOVALIS LINAC system from BrainLAB, Inc., which is a combination of a Varian LINAC and a BrainLAB micro multi-leaf collimator. The NOVALIS accelerator is used for beam shaping only for the situation where beam shapes are provided by the micro multi-leaf collimator used in a conformal beam mode.
The procedure of mounting and de-mounting a miniature multi-leaf collimator from a LINAC requires time and additional quality assurance checks. During the busy daily use of a LINAC for radiation therapy, the steps of mounting and de-mounting a miniature multi-leaf collimator can be inefficient and extend the time of treatment using the miniature multi-leaf collimator. Furthermore, the mounting and de-mounting of a miniature multi-leaf collimator presents a safety hazard, since there is the possibility that improper mounting could lead to the miniature multi-leaf collimator moving or even falling. This could be a safety hazard for the patient who is being treated on the LINAC.
There are other disadvantages of a mountable and de-mountable miniature multi-leaf collimator or a miniature multi-leaf collimator that is mounted permanently and in a fixed position on the LINAC. For example, it may be difficult to use such a collimator to deliver treatments which use combined fields such as miniature multi-leaf conformed fields and larger fields which are shaped by a larger multi-leaf collimator or other radiation shaping devices such as cut blocks, wedges, radiation jaws, and similar devices. In addition, in some clinical applications it is desirable in the treatment of a specific patient at a particular radiation beam angle to use a narrow conformal field, as would be provided by a miniature multi-leaf collimator, and subsequently use a broader field, as would be provided by a multi-leaf collimator.
The present invention is directed to a movable, LINAC-mounted miniature multi-leaf collimator which is adapted so that it can be moved into and out of the general radiation field of the LINAC to provide alternate modes of radiation shaping.
In accordance with one preferred embodiment, a LINAC system includes a miniature multi-leaf collimator which is mounted to the radiation head of a LINAC. The miniature multi-leaf collimator includes a mechanism that translates, rotates or otherwise moves the collimator away from the radiation beam path when the system does not need miniature multi-leaf beam shaping. In this way, beams from a multi-leaf collimator, cut block, or jaws can be delivered to the patient without changing the beam orientation of the LINAC and without removing the miniature multi-leaf collimator physically from the head of the LINAC radiation device. The miniature multi-leaf collimator may be connected to a rail or pivot system which enables the collimator to be swivelled or translated out of the region of the radiation beam when it is not used for conformal beam shaping. A multi-leaf collimator, which is also mounted to the LINAC head, can therefore be used to provide larger conformal fields when the miniature multi-leaf collimator is transposed away from the radiation field.
Advantageously, such a xe2x80x9cpermanentlyxe2x80x9d mounted but movable miniature multi-leaf collimator increases the efficiency of use of the miniature multi-leaf fields and the fields provided by a multi-leaf collimator or other beam-shaping device. Using a single, fixed position of a radiation beam relative to the patient, small conformal fields from the miniature multi-leaf can be delivered, and within seconds the miniature multi-leaf can be translated out of the radiation field, and broader multi-leaf fields can be given to a wider tissue region of the patient. This has the advantage that it improves efficiency and accuracy, allowing concentrated boost fields to tumors to be delivered, and conveniently thereafter, without having to move the beam direction or the patient, delivering broader fields to wider tissue volumes. Advantageously also, the miniature multi-leaf collimator need not be removed from the LINAC, thereby increasing the safety of its use and reducing the chance that the miniature multi-leaf could be accidentally dropped onto the patient or onto the floor, causing injury to the patient or damage to the instrumentation.